1. Field of Invention
This invention relates to a salicide (self-aligned silicide) process.
2. Description of Related Art
Metal silicide is frequently formed on a silicon-based doped region to serve as a contact layer and/or reduce the sheet resistance (Rs). Particularly, nickel salicide can be formed at an anneal temperature below 400° C. so that the underlying doped region can have a shallow junction, and is therefore quite suitable for semiconductor devices of small dimensions.
In a traditional salicide process for forming a metal silicide, a metal layer is formed on a wafer with Si-based regions, a first anneal process is performed to form a metal silicide phase on the Si-based regions, the remaining metal layer is stripped by a selective wet etching process in which a batch of wafers are treated at the same time, and then a second anneal process is performed to change the phase of the metal silicide layer and form a low-resistivity silicide layer. However, the batch-type stripping process suffers from low throughput and poor defect performance.
To increase the throughput and reduce the defect count, a single-wafer tool that treats a single wafer each time can be used in replacement of the wet batch-type tool. However, the sheet resistance of the resulting nickel silicide layer on p+-doped regions is raised by doing so.